1. Field of the Invention
The present invention relates to dryers, and more particularly to a horizontal fluidized-bed dryer having built-in heat transfer tubes.
2. Prior Art
Various horizontal fluidized-bed dryers are known in which wet feed or material to be dried is fluidized in a drying chamber as the wet feed is continuously moved from an inlet side to an outlet side over a porous supporting shelf through which heated air is blown upwardly into the drying chamber. Ideally, it be required that wet feed is in the form of powder in which the individual particles vary in size within a specified range. Practically, however, wet feed is composed of particles which vary in size widely beyond such a specified range, including particles too large to be fluidized. Since such large particles would stay on the supporting shelf so as to close up some of the through-openings therein, circulation of heated air in the drying chamber would be hindered. As a consequence, continuous and efficient drying operation has been difficult to achieve.
To this end, one solution has been proposed by Japanese Patent Publication (Kokoku) No. 48-38495 in which, as illustrated in FIG. 1 of the accompanying drawings, a supporting shelf 12 extends horizontally in a drying chamber 11 and has a multiplicity of through-openings, all inclined in a common direction to deflect the flow of heated air through the shelf 12 so that the large particles are blown progressively from the side of an inlet 13 toward an outlet 14. Although it requires no special mechanism, this prior dryer is useful only under the condition that wet feed does not contain any particle that is larger than a predetermined size.
Another attempt has been proposed by Japanese Patent Publication (Kokoku) No. 50-3225 in which, as illustrated in FIG. 2, a scraper 15 is mounted in the drying chamber 11 in order to push large particles of the wet feed on the supporting shelf 12 toward the outlet 14. With this arrangement, it is possible to discharge the large particles out of the drying chamber with accuracy, irrespective of the size and amount of the large particles. However, since the scraper 15 occupies the major area just over the supporting shelf 12, it is impossible to furnish heat transfer tubes or other parts in that area.